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/*
 * Copyright (c) 2020 PANTHEON.tech, s.r.o. and others.  All rights reserved.
 *
 * This program and the accompanying materials are made available under the
 * terms of the Eclipse Public License v1.0 which accompanies this distribution,
 * and is available at http://www.eclipse.org/legal/epl-v10.html
 */
package org.opendaylight.controller.akka.segjournal;

import static java.util.Objects.requireNonNull;

import com.codahale.metrics.Histogram;
import org.eclipse.jdt.annotation.NonNull;
import org.opendaylight.controller.akka.segjournal.SegmentedJournalActor.ReplayMessages;
import org.opendaylight.controller.akka.segjournal.SegmentedJournalActor.WriteMessages;
import org.opendaylight.controller.akka.segjournal.SegmentedJournalActor.WrittenMessages;

/**
 * Abstraction of a data journal. This provides a unified interface towards {@link SegmentedJournalActor}, allowing
 * specialization for various formats.
 */
abstract class DataJournal {
    // Mirrors fields from associated actor
    final @NonNull String persistenceId;
    private final Histogram messageSize;

    // Tracks largest message size we have observed either during recovery or during write
    private int largestObservedSize;

    DataJournal(final String persistenceId, final Histogram messageSize) {
        this.persistenceId = requireNonNull(persistenceId);
        this.messageSize = requireNonNull(messageSize);
    }

    final void recordMessageSize(final int size) {
        messageSize.update(size);
        updateLargestSize(size);
    }

    final void updateLargestSize(final int size) {
        if (size > largestObservedSize) {
            largestObservedSize = size;
        }
    }

    /**
     * Return the last sequence number completely written to the journal.
     *
     * @return Last written sequence number, {@code -1} if there are no in the journal.
     */
    abstract long lastWrittenSequenceNr();

    /**
     * Delete all messages up to specified sequence number.
     *
     * @param sequenceNr Sequence number to delete to.
     */
    abstract void deleteTo(long sequenceNr);

    /**
     * Delete all messages up to specified sequence number.
     *
     * @param sequenceNr Sequence number to compact to.
     */
    abstract void compactTo(long sequenceNr);

    /**
     * Close this journal, freeing up resources associated with it.
     */
    abstract void close();

    /**
     * Handle a request to replay messages.
     *
     * @param message Request message
     * @param fromSequenceNr Sequence number to replay from, adjusted for deletions
     */
    abstract void handleReplayMessages(@NonNull ReplayMessages message, long fromSequenceNr);

    /**
     * Handle a request to store some messages.
     *
     * @param message {@link WriteMessages} message
     * @return a {@link WrittenMessages} object
     */
    abstract @NonNull WrittenMessages handleWriteMessages(@NonNull WriteMessages message);

    /**
     * Flush all messages to durable storage.
     */
    abstract void flush();
}